The present invention relates to a method for fabricating concrete structures, and in particular, it relates to a method of forming openings in reinforced concrete structures such as manholes.
The use of reinforcing wire in concrete structures is very desirable since the reinforcing wire enhances the strength and integrity of the concrete structure. However, reinforcing wire presents a problem if the concrete structure needs an additional opening to be formed in a wall of the concrete structure. For example, manholes need openings so that sewer pipes may be connected to the interior region of the manhole.
By the term "manhole" it is meant the concrete structure or housing that is positioned within an excavation and into which sewer pipes are connected. Although the construction of the base and the upright wall of the manhole may be the same, the openings that accept sewer pipes have to be custom-positioned depending upon the location of the manhole and the complexity of the sewer system.
Typically what is done to form such openings in a reinforced manhole is that the opening is cut in the reinforcing wire grid at a site where the opening is to be located. A plug having substantially the same thickness as the wall of the manhole is then placed into the cut opening of the reinforcing wire grid and secured thereto. After the manhole is formed, the plug is removed. This method is both time consuming and results in a product that depending on where the opening is located can result in fragility of the structure. It will be appreciated that cutting out a portion of the reinforcing wire grid prior to transporting the manhole to a location where the manhole is to be installed reduces the structural integrity of the manhole and thereby makes it more likely that the manhole will be damaged.
To enhance the structural integrity of the manhole during transportation and installation, certain types of manholes are manufactured without access openings. The access openings are then cut into the manhole when the manhole is installed or ready for installation. A drawback of this approach is that it is considerably more difficult and time consuming to cut the access openings into the manhole after the manhole is fabricated rather than manufacturing the manhole with the access opening.